Certain diesel engines have fuel systems that employ electrically-controlled, hydraulically-activated fuel injectors. Oil that is used as the hydraulic activating fluid for the fuel injectors is supplied under pressure to an oil supply port of each fuel injector. Fuel is supplied to a fuel supply port of each injector. The fuel injector comprises a solenoid that, when energized, causes a fuel charge within the injector body to be injected into an engine cylinder by stroking an intensifier piston within the fuel injector. During an injection of fuel, the solenoid operates a poppet valve within the fuel injector body to communicate the head of the intensifier piston to the pressurized oil. The oil pressure applied to the piston head extends the piston to inject the fuel. When the solenoid is de-energized, the fuel injector is re-charged with fresh fuel as an internal spring retracts the intensifier piston.
A pump whose outlet pressure is regulated by a rail pressure control valve pressurizes the oil that activates the intensifier pistons of the fuel injectors to a controlled rail pressure. Controlling the rail pressure controls the fuel injections from the fuel injectors. The fuel injections are also controlled by controlling the electric current waveforms that energize the fuel injector solenoids.
Increasing the rail pressure may be desirable at certain times for certain reasons. For some emission control purposes, it may be desirable under some circumstances to increase the pressure at which fuel is injected from the fuel injectors. However, because the rail pressure acts on internal mechanisms of the fuel injectors, an increase in the rail pressure may interact with the control relationship between a fuel injector solenoid and its injection mechanism such that an electric current characteristic that produces a certain injector response at a certain rail pressure may not produce the same response at a different rail pressure. Accordingly, it may be appropriate to alter the electric current waveform in a manner that compensates for the effect of changes in rail pressure.
One form that such compensation may take is sometimes referred to as current boost, or simply boost. During an injection of fuel from a fuel injector, boost may be introduced into an electric current waveform that is applied to a fuel injector solenoid. This introduction may comprise increasing the magnitude of the electric current waveform over a portion of the time duration of the waveform. However, increasing the electric current flow to a fuel injector solenoid inherently increases the power flow through electric circuit elements in the electric control that operates the fuel injector. The increased power flow through such circuit elements results in increased power dissipation in them, such power dissipation manifesting itself as heat. Because certain electric circuit elements, such as semiconductors, may be adversely affected by excessive heat, and consequently, increased electric power flow to a fuel injector may be detrimental to the electric control that operates the fuel injectors. Accordingly, special measures may have to be invoked for dissipating the added thermal energy input to the control, such as associating heat sinks with electric circuit components and/or their mountings, and or/ utilizing circuit elements that have higher power ratings. Such solutions are apt to introduce added cost and complexity into a design.
The present invention relates to an improvement that provides a different solution that is believed preferable to those just mentioned. The inventive solution can avoid cost and complexity issues that may be associated with alternative solutions. Briefly, the solution that is embodied in the present invention involves the creation of a combination of selected signal sources that is organized and arranged to control the extent to which a boost signal is allowed to be superimposed on a fuel injection signal waveform applied to a fuel injector. These signal sources include certain variable parameters related to engine operation. Full boost is allowed under sets of conditions where electric circuit elements can tolerate full boost current. Lesser boost is allowed as operating parameters vary in ways that suggest that electric circuit elements are becoming less tolerant.
Several aspects of the invention share the common subject matter of a control for operating an internal combustion engine fuel injector comprising: an injection signal source supplying an injection signal for causing a fuel injector to inject fuel into an engine; a commanded boost signal source supplying a commanded boost signal; and an interface for superimposing the commanded boost signal on the injection signal during a phase of the injection signal.
According to one general aspect of the invention that shares this common subject matter, the commanded boost signal source comprises an is adjusted boost signal source supplying an adjusted boost signal, and the adjusted boost signal source comprises a base boost signal source supplying a base boost signal representing a base boost for the injection signal and a temperature signal source supplying a temperature signal correlated to temperature of an engine operating parameter. The adjusted boost signal is determined both by the base boost signal and by the temperature signal, and the commanded boost signal is determined by the adjusted boost signal.
According to another general aspect that shares the above-mentioned common subject matter, the commanded boost signal source comprises an adjusted boost signal source supplying an adjusted boost signal and a requested boost signal source supplying a requested boost signal. The adjusted boost signal source comprises a base boost signal source supplying a base boost signal representing a base boost for the injection signal, an operating parameter signal source supplying an operating parameter signal correlated to a variable engine operating parameter, and a comparator. The adjusted boost signal is determined both by the base boost signal and by the operating parameter signal, and the comparator determines the commanded boost signal from one of the adjusted boost signal and the requested boost signal to the exclusion of the other.
According to another general aspect that shares the above-mentioned common subject matter, the commanded boost signal source comprises an adjusted boost signal source supplying an adjusted boost signal, and the adjusted boost signal source comprises a base boost signal source supplying a base boost signal representing a base boost for the injection signal and an operating parameter signal source supplying an operating parameter signal correlated to a variable engine operating parameter. The base boost signal source comprises a fuel delivery control signal source supplying a fuel delivery control signal correlated to an amount of fuel to be injected during a fuel injection. The commanded boost signal is determined by the adjusted boost signal, the adjusted boost signal is determined both by the base boost signal and by the operating parameter signal, and the base boost signal is determined by the fuel delivery control signal.
According to another general aspect that shares the above-mentioned common subject matter, the commanded boost signal source comprises an adjusted boost signal source supplying an adjusted boost signal, and the adjusted boost signal source comprises a base boost signal source supplying a base boost signal representing a base boost for the injection signal and an operating parameter signal source supplying an operating parameter signal correlated to a variable engine operating parameter. The base boost signal source comprises an engine speed signal source supplying a speed signal correlated to engine speed. The commanded boost signal is determined by the adjusted boost signal, the adjusted boost signal is determined both by the base boost signal and by the operating parameter signal, and the base boost signal is determined by the engine speed signal.
Still another aspect of the invention relates to an internal combustion engine fuel system comprising: electrically-controlled, hydraulically-activated fuel injectors for injecting fuel into engine cylinders and an electric control for causing hydraulic activation of the fuel injectors to inject fuel into the cylinders. The electric control comprises an injection signal source supplying injection signals to the fuel injectors to cause the fuel injectors to be hydraulically activated, a commanded boost signal source supplying commanded boost signals, and an interface for superimposing the commanded boost signals on the injection signals during phases of the injection signals. The commanded boost signal source comprises an adjusted boost signal source supplying adjusted boost signals, and the adjusted boost signal source comprises a base boost signal source supplying base boost signals representing boost for the injection signals and an operating parameter signal source supplying an operating parameter signal correlated to a variable engine operating parameter. The adjusted boost signals are determined both by the base boost signals and by the operating parameter signal, and the commanded boost signals are determined by the adjusted boost signals.
Still another inventive aspect relates to a method of operating an internal combustion engine fuel injector comprising: creating, in an electric control, a fuel injection signal providing electric power flow to a fuel injector; supplying a commanded boost signal; superimposing the commanded boost signal on the fuel injection signal during a phase of the injection signal to augment the electric power flow to the fuel injector; and attenuating the duration of the commanded boost signal as a function of a variable parameter that is indicative of decreased tolerance of the electric control to increased electric power flow to the fuel injector.
The foregoing, along with further aspects, features, and advantages of the invention, will be seen in this disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, first briefly described below and followed by detailed description.